﻿<p>A structural curve action defines an action which is distributed over a curve.
A curve action may be connected with a curve member or curve connection, or
surface member or surface connection.</p>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC4.
</blockquote>

<blockquote class="change-ifc2x4">
IFC4 CHANGE&nbsp; Former entity <em>IfcStructuralLinearActionVarying</em> from IFC2x2 has been removed and are replaced by this entity.
</blockquote>

<p><b><u>Coordinate Systems</u></b>:</p>

<p>See definitions at <em>IfcStructuralActivity</em>.</p>

<p><b><u>Topology Use Definitions</u></b>:</p>

<p>Standard Case:<br>
If connected with a curve item, instances of <em>IfcStructuralCurveAction</em> shall not have an
<em>ObjectPlacement</em> nor a <em>Representation</em>.  It is implied that the placement and
representation of the <em>IfcStructuralActivity</em> is the same as the ones of the member or
connection.</p>

<p>Special Case 1:<br>
If connected with a surface item, instances of <em>IfcStructuralCurveAction</em> shall have an
<em>ObjectPlacement</em> and <em>Representation</em>, containing an <em>IfcEdgeCurve</em>.  See
<em>IfcStructuralActivity</em> for further definitions.</p>

<p>Special Case 2:<br>
If not connected with a structural item (which may happen in an incomplete or conceptual model),
a curve action should have an <em>ObjectPlacement</em> and <em>Representation</em>, containing an
<em>IfcEdgeCurve</em>.  See <em>IfcStructuralActivity</em> for further definitions.</p>

<p class="spec-head">Informal Propositions:</p>

<ol>
  <li>If the curve action is of the predefined type CONST, SINUS, or PARABOLA,
      <em>SELF\IfcStructuralActivity.AppliedLoad</em> must not be of type
      <em>IfcStructuralLoadConfiguration</em>.  In case of SINUS and PARABOLA, the load item
      defines the maximum of the load at the centre of the load distribution.</li>
  <li>If the curve action is of the predefined type LINEAR,
      <em>SELF\IfcStructuralActivity.AppliedLoad</em> shall be of type
      <em>IfcStructuralLoadConfiguration</em> and shall contain two items.</li>
  <li>If the curve action is of the predefined type POLYGONAL,
      <em>SELF\IfcStructuralActivity.AppliedLoad</em> shall be of type
      <em>IfcStructuralLoadConfiguration</em> and shall contain three or more items.</li>
  <li>If the curve action is of the predefined type DISCRETE,
      <em>SELF\IfcStructuralActivity.AppliedLoad</em> shall be of type
      <em>IfcStructuralLoadConfiguration</em> and shall contain two or more items.</li>
  <li>In case of types LINEAR, POLYGONAL, and DISCRETE, the load items shall have
      one-dimensional <em>IfcStructuralLoadConfiguration.Locations</em>, defining the
      location of the load samples in local coordinates of the curve action.
      The load items shall be provided in ascending order according to their locations.
      The first and the last load item define the extent of the load distribution.</em>
  <li>Point actions must be of type DISCRETE, thus contain two or more load points.
      (Single point loads are modeled by <em>IfcStructuralPointAction</em>.)</li>
  <li>All items in <em>SELF\IfcStructuralActivity.AppliedLoad\IfcStructuralLoadConfiguration.Values</em>
      shall be of the same entity type.</li>
</ol>
